Field of the Disclosure
The present application relates to an organic light emitting diode (OLED) display device and a method driving the same.
Description of the Related Art
Recently, a variety of flat panel display devices with reduced weight and volume to overcome the disadvantages of cathode ray tube (CRT) are being developed. The flat panel display devices include liquid crystal display (LCD) devices, field emission display (FED) devices, plasma display panels (PDPs), electroluminescence devices and so on.
The PDPs have advantages such as a simple manufacture process, lightness and thinness, and are easy to provide a large-sized screen. In view of these points, the PDPs attract consumers' attention. However, the PDPs have serious problems such as low light emission efficiency, low brightness and high power consumption.
Thin film transistor LCD devices are widely used as the flat display devices. However, the thin film transistor LCD devices have disadvantages such as a narrow viewing angle and a low response time.
The electroluminescence display devices are classified into an inorganic light emitting diode display device and an OLED display device on the basis of the formation material of a light emission layer. The OLED display device corresponding to a self-illuminating display device has features such as high response time, high light emission efficiency, high brightness and wide viewing angle.
The OLED display device is configured with a plurality of pixels. Each of the pixels includes an OLED and a cell driver configured to drive each OLED. The OLED includes an anode electrode, a cathode electrode and an organic emission layer interposed between the anode and cathode electrodes. The cell driver generally includes a switching thin film transistor (hereinafter, ‘TFT’), a capacitor and a driving TFT. The switching TFT transfers a data voltage into the capacitor in response to a scan pulse. The driving TFT controls the quantity of light emitted from the OLED by adjusting the current quantity applied to the OLED on the basis of the data voltage which is charged into the capacitor.
An OLED display device and a driving method thereof according to the related art will now be described.
FIG. 1 is a waveform diagram illustrating a method of driving an OLED display device according to the related art. FIG. 2 is a circuit diagram showing an OLED display device of the related art. FIG. 3 is a planar view showing OLED pixels of the related art. FIG. 4 is a cross-sectional view showing a sectional structure of the OLED pixel according to the related art taken along a line a-a′ in FIG. 3.
Referring to FIGS. 1 and 2, each pixel P of the OLED display device according to the related art is driven in such a manner as to be divided into an initialization interval t1, a sampling interval t2, a programming interval t3 and an emission interval t4 according to a timing chain defined by a plurality of pulse signals.
In the initialization interval t1, first and second scan signals SCAN1 and SCAN2 with a high logic level and an emission signal EM with a low logic level are output. The first scan signal SCAN1 and the emission signal EM each have the high logic level, but the second scan signal SCAN2 has the low logic level, during the sampling interval t2. During the programming interval t3, the first scan signal SCAN1 maintains the high logic level but the second scan signal SCAN2 and the emission signal EM each have the low logic level. In the emission interval t4, the emission signal EM with the high logic level and the first and second scan signals SCAN1 and SCAN2 with the low logic level are output.
A second TFT T2 transfers a reference voltage Vinit applied from an initialization voltage supply line Vinit to a second node N2 during the initialization interval t1. To this end, the second TFT T2 is controlled by the second scan signal SCAN2.
In order to apply the reference voltage Vinit to the second node N2 in the initialization interval t1, it is necessary to provide the initialization voltage supply line Vinit.
As shown in FIGS. 3 and 4, each pixel P of the OLED display device according to the related art can include an anode electrode 10, a cathode electrode 20 and an organic emission layer 30 interposed between the anode and cathode electrodes 10 and 20. The initialization voltage supply line Vinit used to apply the reference voltage Vinit to the anode electrode 10 is formed in a region between the pixels P.
Such an initialization voltage supply line used for the anode electrode 10 cannot help but limiting the vertical length of the anode electrode 10. In other words, the anode electrode cannot help but being limited by the initialization voltage supply line on the up and down sides. Due to this, it is difficult to enhance the aperture ratio of the organic emission layer 30.
Moreover, additional circuit components used to apply the initialization voltage (or the reference voltage) Vinit must be included in the OLED display device, which results in the increased size of the bezel region.